1. Field of the Invention
The present invention generally relates to automatically shifting transmissions for bicycles. More specifically, the present invention relates to strategies for controlling the shifting patterns in such transmissions.
2. Related Art
In recent years, bicycles have begun to incorporate automatic transmissions. The automatic transmissions can be either mechanical or electronic in configuration. In the mechanical type transmissions, centrifugal forces are used to change between gears of the transmission. In an electronic type transmission, certain operating characteristics can be sensed and used to signal a desired change between gears. Some of the electronic type transmissions sense operating speed of the bicycle to indicate that a gear change is desired.
The automatic transmissions can be used on bicycles featuring increasing numbers of gear steps through which the transmission can operate. For instance, in bicycles featuring a chain drive with a front sprocket set and a rear sprocket set, the rear sprocket set can comprise ten or more gear steps while the front sprocket can comprise three or more gear steps. The increase in numbers of available gear steps allows a rider to select an appropriate gear combination for any particular riding condition. In addition, when riding a manual transmission bicycle (or in a manual mode), the rider can skip intermediate gears to provide a comfortable shifting pattern.
The large number of available gears, however, causes problems with automatic transmissions. As the rider rapidly increases the speed of the bicycle, the automatic transmission may begin stepping through the gears in rapid succession. It has been found that rapid shifting can be aggravating to the rider. In addition, the lower most gears may not be desired for ordinary use by the rider. Moreover, due to the large number of available gears, the transmission will change gears according to a schedule having very small speed ranges between gear shifts. Thus, the rider may experience shifting even though they are attempting to maintain a steady pace.
Thus, an automatic transmission control system for a bicycle is desired that allows the range of gears to be selected by the rider. The system preferably automatically changes gears within the transmission among a preset range of gears. The rider should be able to change the preset range of gears as desired. The transmission, therefore, will change gears less often and can be adapted for particular riding conditions. As a result of having less gear steps available, the speed ranges associated with each gear step will be enlarged to decrease the likelihood of undesired shifting. To further decrease the likelihood of such gear changes, the system preferably is able to recalibrate the shifting schedule after the rider has achieved a relatively steady pace. Finally, the transmission preferably is able to detect a rapid deceleration and accommodate the downshifting through the gears by reducing the number of gears within the preset range.
Accordingly, one aspect of the present invention involves a control arrangement for a bicycle transmission capable of automatic shifting. The arrangement comprises a transmission having a first set of gear steps and a shift controller that is adapted to move the transmission between each of the first set of gear steps. A control unit is electrically connected to the shift controller. The control unit is adapted to selectively operate the shift controller in an automatic mode using a second set of gear steps selected from the first set of gear steps. The second set of gear steps comprises at least one less gear step than the first set of gear steps. The control unit automatically actuates the shift controller to move the transmission between at least two steps of the second set of gear steps depending upon a sensed operating speed of the bicycle.
Another aspect of the present invention involves a method of controlling shifting in a bicycle transmission capable of automatic shifting. The method comprises sensing an operating speed of the bicycle, monitoring a period of time between transmission shifts, determining when a preset period of time between transmission shifts has elapsed and recalibrating an upper speed value and a lower speed value for a gear step currently in use.
A further aspect of the present invention involves another method of controlling shifting in a bicycle transmission capable of automatic shifting. The method comprises sensing an operating speed of the bicycle, automatically changing gears within a first preset range of gear steps depending upon the operating speed of the bicycle, determining if the operating speed is rapidly reduced below a first threshold operating speed, switching to a second preset range of gear steps when the operating speed is rapidly reduced below the first threshold operating speed, automatically changing gears within the second preset range of gear steps depending upon the operating speed of the bicycle, and the first preset range of gear steps comprising more gear steps than the second preset range of gear steps.
Another aspect of the present invention involves a method of controlling shifting in a bicycle transmission capable of automatic shifting. The method comprising selecting an automatic operating mode, selecting a first preset range of gear steps from a plurality of preset ranges of gear steps, and operating the bicycle transmission among the selected preset range of gear steps.
A further aspect of the present invention involves a bicycle having a transmission capable of automatic shifting. The bicycle comprising a frame, a front wheel rotatably connected to the frame and a rear wheel rotatably connected to the frame. A crank is connected to the frame. A transmission drivingly connects the crank and the rear wheel. A speed sensor is connected to at least one of the front wheel and the rear wheel. A control unit is electrically connected to the speed sensor. A first shift switch and a second shift switch are electrically connected to the control unit. A shift actuator is operably connected to the control unit and to the transmission and is adapted to shift the transmission through a set of gears. The control unit comprises a memory of a first selected set of gears and corresponding shifting speeds, a second selected set of gears and corresponding shifting speeds, and a third selected set of gears and shifting speeds. The first selected set of gears and the second selected set of gears overlap and the second selected set of gears and the third selected set of gears overlap.